1. Field
The present disclosure relates to a polymer-based large-area carbon nanomesh and a method for preparing same. More particularly, it relates to a polymer-based large-area carbon nanomesh prepared using phase separation and cyclization of a polymer via a simple process with high reproducibility, thus being producible in large scale, and a method for preparing same.
2. Description of the Related Art
Graphene is a substance composed of carbon, with atoms arranged in a hexagonal pattern with a planar (2-dimensional) structure, exhibiting properties different from those of graphite or carbon nanotube having a 1-dimensional structure or fullerene having a 0-dimensional structure. It is reported that a single-layer graphene film has unique characteristics distinguished from those of other carbon materials, with a surface area of about 2600 m2/g and an electron mobility of 15,000-200,000 cm2/Vs. In particular, electrons move on the graphene film with a speed close to that of light, because they flow on the graphene film as if they were massless.
The graphene film is mainly prepared by the Scotch tape method, epitaxial growth on silicon carbide, chemical method using a reducing agent or chemical vapor deposition.
The Scotch tape method physically exfoliates a graphene film from graphite using an adhesive tape. Although graphene with a good crystal structure can be obtained easily, the graphene in this way is about tens of micrometers in size and thus is limited in application to electronic devices or electrodes.
The epitaxial method separates carbon from the inside of silicon carbide crystals to the surface at high temperature to form a honeycomb structure peculiar to graphene. This method allows production of graphene films with uniform crystallinity, but electrical properties are relatively inferior to those obtained by other methods. Further, the silicon carbide wafer is very expensive.
The chemical method using a reducing agent involves oxidization of graphite, pulverization of the oxidized graphite to form oxidized graphene and reduction of the oxidized graphene using a reducing agent such as hydrazine. Although this method is advantageous in that the process is simple and carried out at low temperature, the oxidized graphene may not be completely reduced chemically, leading to defects on graphene and consequently poor electrical properties.
Lastly, the chemical vapor deposition deposits a carbon-containing gas at high temperature on a metallic catalyst film on which graphene can grow to obtain graphene films. Although this method allows high-quality large-area graphene films, the procedure of recovering the metallic catalyst film is complicated and difficult.
The graphene prepared in this way is applicable to various fields, from semiconductor devices to flexible electronic devices. However, since graphene is a semi-metal with a zero band gap, its application for a gate for current control in a field-effect transistor (FET) is limited.
In general, there are two methods of controlling the band gap of graphene.
The first method is to cut a single-walled carbon nanotube to obtain a graphene nanoribbon with a width not greater than 10 nm. Although this method provides semiconductor properties by opening of the band gap of graphene, it is inapplicable to commercialization of graphene.
The second method is to prepare a graphene nanomesh using a shadow mask. The method for preparing a graphene or carbon nanomesh involves the following six steps. 1) Graphene is physically exfoliated form graphite and transferred onto a substrate. 2) Under an etching condition, silicon oxide is deposited on the graphene to a thickness of tens of nanometers for selective removal of the graphene and coating of a shadow mask. 3) A block copolymer serving as a shadow mask is coated on the silicon oxide layer and a porous polymer film is prepared through annealing. 4) The silicon oxide layer is selectively removed by injecting reactive ions to result in a pattern similar to that of the porous polymer film. 5) A graphene nanomesh having a pattern similar to that of the resulting silicon oxide layer is prepared by removing exposed graphene using oxygen plasma. In this step, the porous polymer nanofilm is removed by the oxygen plasma treatment. 6) The prepared sample is immersed in hydrofluoric acid to remove the porous silicon oxide layer. Thus prepared graphene nanomesh has a controlled geometry with an inter-pore distance of not greater than 10 nm, thus exhibiting a controlled band gap and semiconductor properties. However, this method realizes the graphene nanomesh on a small piece of graphene and requires a complicated process involving the six steps, as described above. In addition, the reactive ion and oxygen plasma processes are expensive since they require high-vacuum conditions.